Crop rotation can be used to manipulate residue levels under no-tillage in a rainfed Mediterranean-type environment

Fields with low residue levels (<∼2 t ha⁻¹) are prone to erosion and reduced water conservation in semi-arid environments, and high residue amounts (>∼4 t ha⁻¹) can reduce crop establishment and herbicide efficacy. Furthermore, increasing herbicide resistance in southern Australia has resulted in an increase in non-herbicide control measures like ‘windrow burning’, which reduces residue levels. Therefore, it is important to understand crop residue dynamics in this Mediterranean-type environment and any management factors that can be used to regulate amounts of residue. This paper reports on the residue dynamics in a 12-year experiment (2007–2018) in the Wheatbelt of Western Australia, comparing rotations that included: cereal (cereal/cereal/cereal); diverse (wheat/legume/canola); farmer (wheat/barley/break – legume or fallow); and wheat monoculture. Crop residue was either spread behind the harvester (retain) or windrowed at harvest and burnt before seeding (windrow burn). Residue quantity was measured shortly after harvest (usually in December), prior to seeding (usually April), and around anthesis (September).Crop residue amounts were highest after harvest each year and then declined over the next 12 months, until the next harvest. Residue quantity was greatest following years of high rainfall and good crop growth. Within rotations, residue quantity was highest with retained residue in the cereal rotation and wheat monoculture, averaging 5.0 t ha⁻¹ prior to seeding, which could present management problems at seeding time in some years. Residue amounts were lower in the diverse rotation, and levels declined after wheat (4.5 t ha⁻¹) through to legume and canola residue at 3.8 t ha⁻¹. Lowest residue occurred with windrow burning in the farmer rotation, which included one fallow every three years from 2013, with quantities averaging ∼1 t ha⁻¹. Overall, windrow burning before seeding reduced residue amount by ∼50 % compared with retaining the residue.Retaining all residue in a cereal-dominant rotation produced highest residue quantities in this Mediterranean-type environment, but may lead to problems with crop establishment. Residue quantity was reduced to optimal levels by including legume crops or canola in the rotation, as these residues were more rapidly broken down than cereal residues, whilst maintaining residue retention practices.